Variable area convergent/divergent nozzles are used in aircraft gas turbine engines to achieve optimum performance over a wide power range, including afterburning. The discharge nozzle may be vectorable to change the direction of the exhaust gas. Vertical variation will provide pitch control while horizontal variation provides yaw control.
A spherical exhaust nozzle of such capability is shown in U.S. Pat. No. 4,993,641 issued Feb. 19, 1991 to Debora Kehret et al. Static structure conveying the turbine exhaust from the afterburner has a spherical outer surface and an aft opening for the discharge of the gas. Two convergent flaps restrict the gas discharge. The upstream end of each flap surrounds the static structure with the flap having a spherical inside surface.
A seal is required between the static structure and the convergent nozzle. This prevents leakage of the discharge gas outwardly. If cooling air is introduced between the convergent nozzle and the static structure, excess leakage into the turbine exhaust products is avoided. This seal will permit direction of such cooling air into and through the convergent nozzles for cooling thereof.
Brush seals may be used to seal between the two spherical surfaces. FIG. 5 of the above mentioned U.S. Pat. No. 4,993,641 shows a prior art hub structure with a deep narrow annular groove in the hub area. A simple metal ring was located in this groove and held against the static structure with a wave washer. This arrangement leaked badly and caused excessive wear. The seal did not easily follow surface variations.